Calcium phosphate compounds have affinity for a living body (bioaffinity), and sintered bodies thereof have been studied for use as biological materials capable of substituting for bones or teeth.
Inter alia, hydroxyapatite and calcium tertiary .beta.-phosphate are excellent in bioaffinity and harmless to a living body and therefore have attracted attention as substitutes for hard tissues in a living body which can be completely integrated into bones through displacement with new bone. A problem associated with these calcium phosphate compounds is that it takes them from 1 to 3 months to have a sufficient bond strength to hard tissue in a living body.
In an attempt to overcome this problem, it has been proposed to use porous calcium phosphate ceramics. However, having considerably reduced strength, such porous ceramics are of little or no use in application to sites or shapes where mechanical strength is needed.
It is considered that high strength zirconia or alumina having thereon a biologically active calcium phosphate coating would be a high strength ceramic material having biological activity. However, since displacement of the calcium phosphate coating with new bone is necessarily followed by appearance of an interface between a zirconia or alumina body and the new bone, integration with a bone cannot be accomplished. Moreover, plasma spray coating or sputtering, which is a currently employed method for forming a calcium phosphate coating, not only incurs high cost, but is incapable of completely controlling a calcium phosphate phase formed.